Parasitic Infectious Colitis in Dogs

Parasitic Infectious Colitis - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What are Parasitic Infectious Colitis?

The colon is the part of the intestines that is responsible for the last stages of digestion. This stage involves absorbing water from waste products to maintain fluid and electrolyte balance, absorbing nutrients, and storing fecal matter until it is ready to be expelled.  When the lining of the colon becomes overrun with parasites, it can become inflamed and irritated, which disrupts digestion. Secretions of mucus are triggered by the inflammation which then reduces the ability of the colon to absorb water and transport feces.

The type of colitis in dogs that can be caused by a parasitic infection is eosinophilic colitis, which is characterized by an increased number of eosinophils in the gastrointestinal tract. These are white blood cells that attack disease and parasitic infections.

Colitis is an inflammation of the last part of the intestines, namely the colon or large bowel, which causes changes in defecation and stool consistency. There are many reasons why a dog can develop colitis, but when a parasite is involved, it is referred to as parasitic infectious colitis.

Symptoms of Parasitic Infectious Colitis in Dogs

Colitis can be a sudden or ongoing problem. Many of the symptoms you may see in your dog relate to the disruption in absorption and normal gut movement. In chronic cases, a lack of nutrients can lead to worsening symptoms, such as weight loss, lethargy, and a poor overall condition. The main symptom is abnormal stools, which can include:

  • Semi-formed stools
  • Diarrhea 
  • Mucus or fat in stools
  • Slimy or gooey stools
  • Loose, watery stools
  • Stools tinged with blood streaks or flecks
  • Black stools
  • Bright red blood passes after stools are passed

Other symptoms include:

  • Increased defecation
  • Urgency to defecate
  • Decreased volume of stools
  • Straining to defecate
  • Vomiting 
  • Weight loss
  • Passing gas
  • Painful cramping 
  • Inflamed and irritated tissues around anus
  • Dehydration
  • Lack of appetite 
  • Avoid people and other animals
  • Increased amount of sleep
  • Lethargy
  • Poor hair coat 
  • Poor body condition 
  • Visible worms in stools


Colitis is generally divided into acute, episodic, or chronic conditions.

  • Acute colitis occurs suddenly and often resolves within a few days; symptoms of diarrhea and cramping do not last long, and the affected dog quickly returns to normal
  • Episodic colitis is more sporadic, causing symptoms that appear for a few weeks, then disappear, only to reappear again later
  • Chronic colitis is when symptoms last for several weeks, months, or even years; the severity of the symptoms usually worsen as the condition continues

Causes of Parasitic Infectious Colitis in Dogs

There are many reasons why a dog can develop colitis, including infections, trauma, stress, allergies, and underlying internal diseases. When a dog is diagnosed with parasitic infectious colitis, then the cause of the colitis is a parasitic infection. The infecting parasite can include:

  • Giardia
  • Cryptosporidium
  • Whipworms
  • Coccidia
  • Tapeworms 
  • Roundworms 

Your dog can become infected with a parasite through:

  • Ingestion of eggs or larvae 
  • Contact with other infected animals
  • Contact with infected stools, food, water, soil, or objects
  • From mother to puppy in utero or through nursing
  • Fleas

Diagnosis of Parasitic Infectious Colitis in Dogs

If your dog is having elimination problems, your veterinarian will perform a physical exam and ask you many questions about your dog’s symptoms and medical history, as well as any exposure to possible infectious agents. There can be many causes for symptoms of intermittent and bloody diarrhea, and testing can help your veterinarian determine the one that is affecting your dog.

During an exam, your veterinarian may palpate your dog’s rectal and abdominal areas. Blood work, including a CBC, a urinalysis, and fecal testing are performed. A CBC may reveal eosinophilia, a sign of possible parasitic infection. Fecal smears and flotation can reveal the presence of parasites. If these results are not definitive, then further testing can be performed, such as ultrasounds and X-rays to examine the colon for any masses, enemas, cultures, and a colonoscopy. This procedure can both examine the colon lining and collect biopsy samples for testing, and can also reveal the presence of parasites in the colon.

Treatment of Parasitic Infectious Colitis in Dogs

Once your dog has been diagnosed with parasitic infectious colitis, treatment includes controlling the parasites, diet management to help your dog’s gastrointestinal system return to normal, and supportive medications to aid in his recovery.

Parasite Control

Your dog will generally be prescribed a deworming medication to kill the parasites that have caused the colitis. Fenbendazole and metronidazole are common medications given, and are repeated after three weeks from the first dose even if further diagnostic testing reveals no signs of the parasites. They may be repeated again in three months. 


To help your dog’s gastrointestinal system relax and return to normal function, a fast is often prescribed for 24 to 48 hours. Then, fiber is added to a bland diet to bulk up stool and encourage useful bacteria to grow. If your veterinarian believes there is another problem happening with your dog that is contributing to the colitis, he may prescribe a special diet, such as a hypoallergenic, novel, or hydrolyzed diet. 

Supportive Medications

Additional medications may be prescribed to help your dog’s recovery. These can include anti-inflammatory drugs, such as sulphasalazine or prednisolone, antibiotics, antimicrobials, glucocorticoids, and immunosuppressive drugs.

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Recovery of Parasitic Infectious Colitis in Dogs

If the parasites are eliminated, recovery from parasitic infectious colitis is good. After treatment and a supportive diet, your dog can return to normal digestive function. If the colitis is chronic and does not disappear after treatments, further testing may be needed to assess if there is another underlying reason for the condition.

Parasites are easily spread from infected to healthy dogs, and prevention is needed to ensure that your dog does not get re-infected, or does not infect others. Limit contact with new animals, and routinely deworm your dog, especially if his risk is high. Talk with your veterinarian about spot treatments and chews that can protect your dog from an infection.

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© 2024 Wag Labs, Inc. All rights reserved.